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Analog Devices Inc. LT8709IFE#TRPBF
- Part No.:
- LT8709IFE#TRPBF
- Manufacturer:
- Analog Devices Inc.
- Category:
- DC DC Switching Controllers
- Package:
- 20-TSSOP (0.173", 4.40mm Width) Exposed Pad
- Datasheet:
-
LT8709IFE#TRPBF.pdf
- Description:
- IC REG CTRLR MULT TOP 20TSSOP
- Quantity:
- Payment:
- Shipping:
Inventory:3,302
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Product details
Overview
LT8709IFE#TRPBF from Analog Devices (formerly Linear Technology) is a synchronous PWM controller for negative-to-negative or negative-to-positive DC/DC conversion, featuring rail-to-rail output current monitoring and control. It supports buck, boost, buck-boost, and inverting topologies with –4.5V to –80V input range, 100kHz–750kHz switching frequency, and operates across –40°C to 125°C junction temperature. It is used in telecom power supplies and cathodic protection systems.
For engineers reviewing the LT8709IFE#TRPBF datasheet, LT8709IFE#TRPBF pinout, LT8709IFE#TRPBF application, or LT8709IFE#TRPBF equivalent, key selection considerations include its negative-input capability, MODE-pin-selectable CCM/DCM operation, rail-to-rail IMON output, EN/FBIN input regulation, and 20-lead TSSOP package with exposed –VIN pad.
Technical Context
The LT8709IFE#TRPBF integrates dual error amplifiers (FBY and IMON paths), a programmable oscillator with RT/SYNC interface, and independent gate drivers for high-side PFET (TG) and low-side NFET (BG). Its EN/FBIN pin provides both enable control and input voltage regulation to prevent collapse of high-impedance negative sources.
It features three distinct operating modes: forced CCM (via MODE pin <1.175V), pulse-skipping DCM (MODE >1.224V), and automatic transition based on load and SS/INTVEE status. Current sensing uses Kelvin-connected ISP/ISN pins with 50mV typical full-scale sense voltage and integrated transconductance amplifier (A7 = 1000 µS).
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input Voltage Range | –4.5V to –80V: Enables direct use with legacy telecom –48V, –60V, or industrial negative rails without pre-regulation. |
| Switching Frequency | 100kHz to 750kHz: Adjustable via RT resistor or external SYNC clock; supports EMI optimization and magnetics size reduction. |
| Output Current Sense Accuracy | ±5% over temperature: Achieved via rail-to-rail IMON output (11.9× gain + 51.8mV offset) for precise battery/capacitor charging control. |
| Operating Temperature | –40°C to 125°C junction: Validated for industrial and telecom equipment deployed in uncontrolled ambient environments. |
| Package | 20-lead TSSOP with exposed –VIN pad: Provides thermal path to PCB plane; requires soldering exposed pad to –VIN copper for thermal and electrical integrity. |
| Power Good Threshold | ±74.9µA (negative FBY) / ±75.4µA (positive FBY): Corresponds to ~90% output regulation voltage; includes 100µs anti-glitch delay for stable system sequencing. |
| EN/FBIN Regulation Range | 1.55V to 1.662V: Enables active input voltage regulation to maintain stable operation when sourcing from high-impedance negative supplies. |
Pinout & Package
LT8709IFE#TRPBF is housed in a 20-lead plastic TSSOP package (FE grade) with exposed pad (Pin 21) electrically connected to –VIN. The exposed pad must be soldered to a local –VIN PCB plane for thermal management and reference integrity.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| –VIN (Pins 20, 21) | Negative input supply and substrate reference | Primary power rail and chip ground reference; exposed pad (Pin 21) must be soldered to –VIN copper for thermal conduction and noise immunity. |
| FBY (Pin 1) | Feedback input for output voltage regulation | Voltage-referred-to-GND; supports both negative (–1.234V typ) and positive (–15.8mV typ) output configurations via single-resistor divider. |
| VC (Pin 2) | Error amplifier output | Drives external compensation network between VC and –VIN; sets duty cycle to regulate VOUT via FBY loop. |
| PG (Pin 4) | Power good open-drain output | Active-high signal indicating FBY current within 90% regulation window; requires external pull-up to –VIN or BIAS. |
| IMON (Pin 5) | Output current monitor output | Voltage proportional to ISP–ISN (VIMON = 11.9 × (VISP–VISN) + 616mV); enables real-time current telemetry and closed-loop charging. |
| ISP/ISN (Pins 6, 7) | Kelvin current sense inputs | Detect average output current via external sense resistor; full-scale differential = 50mV (typ), enabling accurate current limiting at 8.5A output. |
| BIAS (Pin 8) | Secondary positive supply and TG driver rail | Provides high-voltage rail for PFET gate drive; must be bypassed to –VIN; connects to VOUT (inverting), INTVCC (boost), or GND (buck). |
| INTVEE (Pin 9) | TG driver bottom rail regulator | 6.18V below BIAS; enables TG switching when BIAS–INTVEE >3.42V; bypassed to BIAS with ≥2.2µF capacitor. |
| TG (Pin 10) | High-side PFET gate driver output | Swings between BIAS and BIAS–INTVEE; drives external P-channel MOSFET in buck, boost, or inverting topologies. |
| BG (Pin 11) | Low-side NFET gate driver output | Swings between –VIN and INTVCC (6.3V); drives external N-channel MOSFET; non-overlap timing prevents shoot-through. |
| GND (Pin 13) | Positive input supply reference | Local positive rail; must be bypassed to –VIN; functional down to V–VIN if BIAS–V–VIN >4.5V. |
| CSP/CSN (Pins 14, 15) | NFET switch current sense inputs | Monitor peak switch current for cycle-by-cycle limiting; full-scale sense voltage = 50mV (typ) at minimum duty cycle. |
| EN/FBIN (Pin 16) | Enable and input regulation input | Enables chip above 1.7V; regulates input current between 1.55V–1.662V; hysteresis = 44mV; must not be left floating. |
| MODE (Pin 17) | CCM/DCM mode select | Forced CCM if <1.175V; DCM/pulse-skipping if >1.224V; hysteresis = 49mV; overrides light-load behavior when asserted. |
| RT (Pin 18) | Oscillator timing resistor input | Resistor from RT to –VIN sets free-running frequency (e.g., 46.4kΩ → 750kHz, 357kΩ → 100kHz); no internal pull-up/down. |
| SYNC (Pin 19) | External clock synchronization input | Accepts external clock (1.5V–5.5V logic levels); overrides internal oscillator; duty cycle 20%–80% supported. |
| SS (Pin 3) | Soft-start capacitor node | Charged by internal 260kΩ current source to ~2.7V; discharged during UVLO, overcurrent, or overtemperature for auto-restart. |
| INTVCC (Pin 12) | Internal 6.3V LDO output | Supplies BG driver and logic; sourced from GND or BIAS; UVLO threshold = 3.88V rising; max 5mA external load. |
Key Features
| Feature | Design Value |
|---|---|
| Rail-to-rail output current monitor (IMON) | Delivers 0–1.213V output for 0–50mV ISP–ISN range, enabling precision current telemetry and closed-loop battery charging without external op-amps. |
| Input voltage regulation via EN/FBIN | Maintains stable operation from high-impedance negative sources (e.g., long cables, aging batteries) by dynamically limiting NFET current before input collapse. |
| Topology flexibility with single feedback pin | Supports buck, boost, buck-boost, and inverting configurations using only FBY pin-no topology-specific pins or external logic required. |
| MODE-pin-selectable CCM/DCM operation | Forces continuous conduction mode for low-noise applications or enables pulse-skipping for >90% light-load efficiency-user-configurable per system needs. |
| Integrated frequency foldback | Reduces switching frequency to 1/5 nominal under overload or thermal stress, lowering power loss and improving reliability during fault conditions. |
| Thermal shutdown and soft-start reset | Auto-restarts after overtemperature (TJ >175°C) or overcurrent events via SS pin discharge-no external circuitry needed for robust fault recovery. |
Applications
| Telecom Power Conversion | Cathodic Protection Systems |
|---|---|
|
Use Scenario: Converting –48V or –60V telecom distribution rail to regulated –12V/8.5A for line card power. IC Role / Device Role / Timing Role: Synchronous negative-input buck controller managing high-current delivery with minimal heat rise. Use Value: Achieves >95% efficiency at full load while maintaining tight output regulation across –40°C to 70°C ambient, reducing cooling requirements. |
Use Scenario: Generating high-current negative output (e.g., –12V @ 8.5A) to protect buried pipelines from electrochemical corrosion. IC Role / Device Role / Timing Role: Negative-input, negative-output DC/DC controller with precise current limiting for constant-current anode drive. Use Value: Rail-to-rail IMON output enables real-time current monitoring and closed-loop adjustment to maintain protective current density within ±1% tolerance. |
| Negative Input to Positive Output Supplies | Industrial High-Voltage Negative Rails |
|
Use Scenario: Deriving +12V/5A from a –24V industrial bus for isolated sensor interfaces or analog front-ends. IC Role / Device Role / Timing Role: Inverting topology controller using single FBY feedback and integrated TG/BG drivers. Use Value: Eliminates need for external level-shifting or isolated controllers-reduces BOM count and layout complexity by 30% vs. discrete solutions. |
Use Scenario: Powering test equipment requiring stable –72V bias supply from a –80V primary source with tight ripple and transient response. IC Role / Device Role / Timing Role: Wide-input negative-input buck controller supporting up to –80V input with 100kHz–750kHz adjustable frequency. Use Value: Programmable RT-based frequency tuning allows optimization for low EMI (<150mVpp) in sensitive measurement environments. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar negative-input DC/DC controller applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| LTC7804 | Positive-input synchronous controller; no native negative-input support; requires external level-shifting for –VIN operation. | Suitable for positive-input boost/buck-boost but not direct replacement for –48V input telecom supplies. | Select LTC7804 only when redesigning for positive-input architecture; LT8709IFE#TRPBF avoids level-shift complexity and maintains negative-rail integrity. |
| LT8390A | Wide-input (–4V to 120V) synchronous controller with integrated gate drivers; supports negative input but lacks rail-to-rail IMON output. | Can replace LT8709IFE#TRPBF in buck or inverting topologies but requires external current-sense amplifier for battery charging accuracy. | Choose LT8390A when higher input voltage range (>–80V) is critical; retain LT8709IFE#TRPBF when IMON-based current telemetry is mandatory. |
Compared with LTC7804 and LT8390A, the LT8709IFE#TRPBF uniquely combines native negative-input operation, rail-to-rail IMON telemetry, and single-pin topology configuration-enabling simpler, more reliable designs for telecom, cathodic protection, and industrial negative-rail systems without external signal conditioning.
Availability
LT8709IFE#TRPBF is available at Aetrix Electronics and suitable for telecom equipment power supplies, cathodic protection systems, and industrial high-voltage negative rail applications requiring stable component supply, extended temperature operation, and long-term lifecycle continuity.
Supply support for LT8709IFE#TRPBF includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.
Manufacturer
Analog Devices, Inc. (acquired Linear Technology in 2017) is a global leader in high-performance analog, mixed-signal, and power management semiconductors, serving industrial, automotive, communications, and healthcare markets.
The LT8709IFE#TRPBF belongs to Linear's high-voltage negative-input controller product line, designed specifically for robust, efficient power conversion in legacy telecom infrastructure, corrosion protection, and industrial systems with demanding negative-rail requirements.
FAQ
What is the absolute maximum input voltage rating for the LT8709IFE#TRPBF?
The LT8709IFE#TRPBF has an absolute maximum rating of –80V on the –VIN pin relative to GND. Exceeding this voltage may cause permanent damage. The recommended operating range is –4.5V to –80V, and the device includes undervoltage lockout (UVLO) that activates below –4.5V input to prevent erratic operation. Always observe the –VIN pin's absolute maximum rating during transient conditions.
How does the EN/FBIN pin function in input voltage regulation mode for the LT8709IFE#TRPBF?
The EN/FBIN pin on the LT8709IFE#TRPBF provides dual functionality: chip enable and active input voltage regulation. When the EN/FBIN voltage is between 1.55V and 1.662V (typ), the internal amplifier regulates NFET current to prevent collapse of high-impedance negative sources. This is distinct from simple enable/disable-regulation occurs dynamically to maintain stable input voltage under varying load conditions.
Can the LT8709IFE#TRPBF be used in a positive-output configuration from a negative input?
Yes, the LT8709IFE#TRPBF supports positive-output configurations (e.g., –24V to +12V) using boost or inverting topologies. The FBY pin accepts either negative or positive feedback signals: for positive outputs, FBY regulation is set to –15.8mV (typ), and the feedback resistor network connects accordingly. The integrated TG/BG drivers and MODE pin ensure correct switching behavior regardless of output polarity.
What is the purpose of the exposed pad (Pin 21) on the LT8709IFE#TRPBF package?
The exposed pad (Pin 21) on the LT8709IFE#TRPBF is electrically connected to –VIN and serves as the primary thermal and electrical return path. It must be soldered to a dedicated –VIN copper plane on the PCB to ensure proper thermal dissipation (θJA = 38°C/W) and minimize noise coupling into sensitive analog blocks like the IMON and FBY amplifiers. Leaving it unconnected degrades thermal performance and may cause instability.
Does the LT8709IFE#TRPBF support external clock synchronization, and what are the voltage thresholds?
Yes, the LT8709IFE#TRPBF supports external clock synchronization via the SYNC pin (Pin 19). A logic-high SYNC signal must exceed 1.5V (min), and logic-low must be below 0.4V (max), both referenced to –VIN. The SYNC input accepts duty cycles from 20% to 80%, and frequencies within the 100kHz–750kHz operating range. Driving SYNC below 0.4V reverts the controller to its internal RT-set frequency.
LT8709IFE#TRPBF Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- -
- Package/Case:
- 20-TSSOP (0.173", 4.40mm Width) Exposed Pad
- Packaging:
- Tape & Reel (TR)
- Product Status:
- Active
- Output Type:
- Transistor Driver
- Function:
- Step-Up, Step-Down, Step-Up/Step-Down
- Output Configuration:
- Positive or Negative
- Topology:
- Buck, Boost, Buck-Boost
- Number of Outputs:
- 1
- Output Phases:
- 1
- Voltage - Supply (Vcc/Vdd):
- -4.5V ~ -80V
- Frequency - Switching:
- 100kHz ~ 750kHz
- Duty Cycle (Max):
- -
- Synchronous Rectifier:
- Yes
- Clock Sync:
- Yes
- Serial Interfaces:
- -
- Control Features:
- Enable, Frequency Control, Power Good, Soft Start
- Operating Temperature:
- -40°C ~ 125°C (TJ)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 20-TSSOP-EP
LT8709IFE#TRPBF FAQ
1.How can I place an order for LT8709IFE#TRPBF through Aetrix?
Please submit a Request for Quotation (RFQ) for LT8709IFE#TRPBF on Aetrix. Our sales agent will provide a competitive quotation and guide you through the order confirmation once you accept the terms.
2.Are the price and stock information for LT8709IFE#TRPBF reliable?
The price and inventory of LT8709IFE#TRPBF are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT8709IFE#TRPBF is usually 5 days.
3.What payment methods are accepted for LT8709IFE#TRPBF?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT8709IFE#TRPBF transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT8709IFE#TRPBF?
LT8709IFE#TRPBF orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT8709IFE#TRPBF order is processed, you will receive an email with the shipment details and tracking number.
Note: Tracking information may take up to 24 hours to appear. Express delivery typically takes 3–5 business days.
5.How can I obtain technical support or documentation for LT8709IFE#TRPBF?
For technical support, including LT8709IFE#TRPBF datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT8709IFE#TRPBF requirements.
6.How does Aetrix verify that LT8709IFE#TRPBF is sourced from the original manufacturer or authorized distributors?
All LT8709IFE#TRPBF products on Aetrix are procured from qualified distributors and authorized channels. Our dedicated quality assurance team conducts strict verification, including traceability checks and, if necessary, third-party testing. This ensures that LT8709IFE#TRPBF meets industry standards.
7.What is the process for return or replacement of LT8709IFE#TRPBF?
All LT8709IFE#TRPBF units undergo pre-shipment inspection (PSI). If there is an issue with LT8709IFE#TRPBF, returns or replacements are accepted under the following conditions:
1.Quantity discrepancies, incorrect items, or visible external defects (such as breakage or corrosion), acknowledged by Aetrix.
2.The issue is reported within 90 days of delivery.
3.The LT8709IFE#TRPBF part is unused and in its original packaging.
Return procedure for LT8709IFE#TRPBF:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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